Studies from our laboratory have characterized sodium-calcium exchange (Na:Ca) activity in afferent and efferent arterioles and cultured mesangial cells from Dahl/Rapp salt sensitive (S) and salt resistant (R) rats. We have identified a difference in protein kinase C (PKC) regulation of Na:Ca exchange in both afferent arterioles and mesangial cells from S compared to R rats. Specifically, phorbol esters that activate PKC enhance Na:Ca exchange in R, but not in S rats. Also, Na:Ca exchange activity appears to be specifically depressed in afferent arterioles from S rats on a 8.0% NaCl diet compared to R rats on a high salt diet or S and R rats on a low Na diet. The present studies will characterize and evaluate the regulation of Na:Ca exchange in S, R and Sprague Dawley (SD) rats, and will determine if alterations in Na:Ca exchange are related to the development of salt-sensitive hypertension. Studies will be performed in isolated afferent and efferent arterioles and cultured mesangial cells. S, R and SD rats will be maintained on a low (0.3%) or high (8.0%) NaCl diet for one week and awake blood pressures will be determined. Photometry and image analysis fluorescence microscopy will be used to measure alterations in [Ca] using Fura 2, [Na]i using SBFl and Na-Green. Cell membrane potential will be measured using patch clamp techniques and PKC activity will be assayed in cultured mesangial cells and in smooth muscle cells obtained from the renal microvasculature. Additional studies will correlate changes in [Ca] with contractility by assessing alterations in arteriolar diameter and changes in mesangial cell shape. These studies will be performed to: 1) evaluate and compare endogenous Na:Ca exchange activity and the effect of exchange activity on contractility in S, R and SD arterioles and mesangial cells; 2) further investigate differences in PKC regulation of the exchanger in S versus R and SD rats, and to identify other cellular regulators such as (Ca]i, membrane potential and other kinases which may influence Na:Ca exchange activity. Other studies will evaluate regulation of the exchanger by agonists including angiotensin II, U46619, endothelin and nitric oxide; 3) assess Na:Ca exchange activity and its regulation in rats fed 0.3% or 8.0% NaCl +/- dietary L-arginine supplementation; and 4) determine if alterations in Na:Ca exchange activity correlate with blood pressure in the F2 generation of Dahl/Rapp rats. These studies will provide new information concerning a potential defect in Na:Ca exchange that may have important implications in the pathogenesis of salt-sensitive hypertension in Dahl/Rapp rats.